Commercial services which employ a W-CDMA (Wideband Code division Multiple Access) method which is included in communication methods called a third generation were started in Japan since 2001. Furthermore, a start of a service with HSDPA (High Speed Down Link Packet Access) which implements a further improvement in the speed of data transmission using downlinks (an individual data channel and an associated control channel) by adding a channel for packet transmission (HS-DSCH: High Speed-Downlink Shared Channel) to the downlinks has been planned. In addition, an HSUPA (High Speed Up Link Packet Access) method has also been suggested and studied in order to speed up uplink data transmission.
The W-CDMA is a communication method which was determined by the 3GPP (3rd Generation Partnership Project) which is the organization of standardization of mobile communication systems, and the technical specification of the release 6 has been being organized currently.
In the 3GPP, as a communication method different from the W-CDMA, a new communication method having a wireless section, which is referred to as “Long Term Evolution” (LTE), and a whole system structure including a core network, which is referred to as “System Architecture Evolution” (SAE), has been studied.
The LTE has an access method, a radio channel configuration, and protocols which are different from those of the current W-CDMA (HSDPA/HSUPA). For example, while the W-CDMA uses, as its access method, code division multiple access (Code Division Multiple Access), the LTE uses, as its access method, OFDM (Orthogonal Frequency Division Multiplexing) for the downlink direction and uses SC-FDMA (Single Career Frequency Division Multiple Access) for the uplink direction. Furthermore, while the W-CDMA has a bandwidth of 5 MHz, the LTE can have a bandwidth of 1.25/2.5/5/10/15/20 MHz. In addition, the LTE uses only a packet communication method, instead of a circuit switching method which the W-CDMA uses.
According to the LTE, because a communication system is constructed using a new core network different from a core network (General Packet Radio System GPRS) which complies with the W-CDMA, the communication system is defined as an independent radio access network which is separate from a W-CDMA network. Therefore, in order to distinguish from a communication system which complies with the W-CDMA, in a communication system which complies with the LTE, a base station (Base station) which communicates with a mobile terminal UE (User Equipment) is called eNB (E-UTRAN NodeB, eNodeB, or eNode-B), a base station control apparatus (Radio Network Controller) which performs exchange of control data and user data with a plurality of base stations and is called an aGW (Access Gateway).
This communication system which complies with the LTE carries out point-to-multipoint (Point to Multipoint) communications, such as a multicast and broadcast type multimedia service called a E-MBMS (Evolved Multimedia Broadcast Multicast Service), and also provides a communication service such as a unicast (Unicast) service for each mobile terminal among a plurality of mobile terminals.
In the case of the LTE, because no individual channels (Dedicated Channel and Dedicated Physical Channel) destined for each mobile terminal exist in transport channels and physical channels, transmission of data to each mobile terminal is carried out by using a common channel (Shared channel), unlike in the case of the W-CDMA.
When receiving data, via a downlink, from a base station, a mobile terminal transmits a signal indicating whether the mobile terminal has received the data perfectly, and a signal indicating either the quality of the received data or the quality of the downlink communication path to the base station via an uplink. The response signal indicating whether the mobile terminal could receive the data correctly from the base station is referred to as an Ack/Nack, and the quality information indicating the quality of the received data or the quality of the downlink communication path is referred to as a CQI (Channel Quality Indicator).
An Ack/Nack is a signal with which, when the mobile terminal has received downlink data, the mobile terminal notifies information indicating whether the mobile terminal could receive the downlink data correctly to the base station, and the base station uses the Ack/Nack for retransmission control.
A CQI is a signal with which the mobile terminal notifies the downlink channel's state (the communication path's state) which the mobile terminal has measured to the base station, and the base station uses the CQI for downlink scheduling. Furthermore, when data which the mobile terminal has to transmit to the base station occur, the mobile terminal transmits a signal with which to make a request for allocation of uplink radio resources to the base station. Such a request signal is called a scheduling request, an uplink resource request, or an uplink scheduling request signal (SR: Scheduling Request). The Ack/Nack, the CQI, and the SR as mentioned above are called “uplink L1/L2 control signals” (an L1/L2 control signaling).
FIG. 22 is an explanatory drawing for explaining uplink L1/L2 control signals.
As shown in FIG. 22, uplink L1/L2 control signals are roughly divided into two types of L1/L2 control signals. They are uplink-data-associated L1/L2 control signals (a data-associated L1/L2 control signaling), and uplink-data-non-associated L1/L2 control signals (a data-non-associated L1/L2 control signaling).
An uplink-data-associated L1/L2 control signal is information required for uplink data transmission (reception by a base station), such as a transport format, and is transmitted together with uplink data. Uplink-data-non-associated L1/L2 control signals include an Ack/Nack and a CQI which are relevant to a downlink, and random access (Random Access) signals, such as a scheduling request (SR, UL SR) which is transmitted before uplink data transmission is started.
Although an Ack/Nack and a CQI are transmitted regardless of uplink data transmission because they are relevant to a downlink, there is a case in which they are transmitted at the same time when uplink data are transmitted. On the other hand, random access signals include a synchronous random access (Synchronous Random Access which is referred to as SRA from here on) signal and a non-synchronous random access (Non-Synchronous Random Access which is referred to as NSRA from here on) signal.
An SRA is transmitted in a state in which uplink time synchronization is established, whereas an NSRA is transmitted in a state in which uplink time synchronization is not established.
Not only uplink-data-associated L1/L2 control signals but also an Ack/Nack and a CQI are transmitted in a state in which uplink time synchronization is established. Hereafter, the fact that there is a state in which an Ack/Nack and/or a CQI, and an SRA in a case in which no uplink data transmission is carried out are transmitted simultaneously will be mentioned, and a problem with this state and a solution of this problem will be mentioned.
An uplink Ack/Nack and an uplink CQI are relevant to a downlink. For allocation of an Ack/Nack and a CQI to physical resources to in the case in which no uplink data transmission is carried out, a method of monopolistically allocating one certain time-frequency region or a method of monopolistically allocating a plurality of time-frequency regions having separated narrow bands is used (for example, refer to nonpatent reference 1).
Hereafter, these regions are referred to as an Ack/Nack exclusive channel.
That is, in a state in which uplink data transmission is not performed, an Ack/Nack and a CQI are transmitted by using an Ack/Nack exclusive channel.
In further explaining in detail, (1) in a case in which both an Ack/Nack and a CQI have to be transmitted, the Ack/Nack and the CQI are transmitted by using an Ack/Nack exclusive channel, (2) in a case in which an Ack/Nack has to be transmitted, but a CQI does not have to be transmitted, the Ack/Nack is transmitted by using an Ack/Nack exclusive channel, and (3) in a case in which an Ack/Nack does not have to be transmitted, but a CQI has to be transmitted, the CQI is transmitted by using an Ack/Nack exclusive channel. It can also be considered that, (4) even in a case in which an Ack/Nack does not have to be transmitted, and a CQI does not have to be transmitted, an Ack/Nack exclusive channel is allocated to them. In this case, both no Ack/Nack and no CQI are transmitted by using the above-mentioned channel.
FIG. 23 is an explanatory drawing showing radio resources to which an Ack/Nack and a CQI are allocated in the case in which uplink data transmission is carried out or in the case in which no uplink data transmission is carried out. FIG. 23 shows the method of monopolistically allocating one certain time-frequency region.
An Ack/Nack and a CQI in the case in which no uplink data transmission is carried out are allocated to a region having one or more subframes with respect to time and are allocated to a region having one or more resource units with respect to frequency. In contrast, uplink data, and an Ack/Nack and a CQI in the case in which transmission of either an uplink-data-associated L1/L2 control signal or the uplink data is carried out are allocated to another region.
By allocating an Ack/Nack and a CQI in the case in which no uplink data transmission is carried out, i.e., signals associated with only an Ack/Nack and a CQI to a monopolistic region intended only for the signals, a time during which the Ack/Nack and CQI signals are transmitted can be increased, and therefore a large coverage can be acquired.
FIG. 24 is an explanatory drawing showing radio resources in which an Ack/Nack and a CQI are allocated to an Ack/Nack exclusive channel. FIG. 24 shows the method of monopolistically allocating a plurality of time-frequency regions (A and B in FIG. 24) having separated narrow bands for an Ack/Nack and a CQI.
An Ack/Nack and a CQI in the case in which no uplink data transmission is carried out are allocated to some separated regions in units of a subframe with respect to time and are allocated to some separated regions in units of a subcarrier with respect to frequency. By separating the frequency region into some parts (e.g., A and B in FIG. 24), a frequency diversity gain can be acquired.
When using either of the methods, an Ack/Nack and a CQI of one or more mobile terminals can be allocated to one region. It has been studied to, in order to implement a method of multiplexing an Ack/Nack and a CQI of one or more mobile terminals into one region, establish the orthogonality of each mobile terminal by using FDM (Frequency Division Multiplex)/TDM (Time Division Multiplex)/CDM (Code Division Multiplex). In order to ensure the quality of reception of an Ack/Nack and a CQI by a base station, it has been studied to increase the power by carrying out repetition (repetition) transmission of the Ack/Nack and the CQI. More specifically, there are a method of repeatedly transmitting the same subframe twice within one transmission time interval (Transmission Time Interval TTI), a method of repeatedly including a bit of an Ack/Nack and a bit of a CQI to a plurality of LBs (Long Block) in a subframe so as to transmit them, and so on.
A synchronous random access (Synchronous Random Access SRA) is a signal used for a scheduling request (SR) which a mobile terminal transmits before starting uplink data transmission, which the mobile terminal transmits when the mobile terminal is placed in a state in which uplink time synchronization is established (in other words, the mobile terminal is placed in an Active mode). As a method of allocating an SRA to physical resources, there is provided a method of monopolistically allocating one certain time-frequency region (Nonpatent reference 3: TR25.814V7.0.0). FIG. 25 is an explanatory drawing showing radio resources in which an uplink scheduling request signal is allocated to an S-RACH. FIG. 25 shows the method of monopolistically allocating one certain time-frequency region.
An SRA is allocated to a region in units of a subframe with respect to time and is allocated to a region in units of one or more resource units with respect to frequency. Hereafter, these regions are referred to as an S-RACH (Synchronous Random Access CHannel). In contrast, uplink data are allocated to other regions. Therefore, an SRA and data are multiplexed with respect to either or both of time and frequency.
With which region a mobile terminal transmits an SRA is predetermined or is notified in advance from a base station. An SRA of one or more mobile terminals is allocated to one region. When transmissions of SRAs of a plurality of mobile terminals occur with an identical region, the signals from the plurality of mobile terminals will collide with one another.
When the SRAs from the plurality of mobile terminals collide with one another and therefore the base station cannot receive them, each of the plurality of mobile terminals generally repeats transmission of its SRA again with either or both of a different periodicity and a different region. In order to reduce the probability that SRAs from a plurality of mobile terminals collide with one another, a method of establishing the orthogonality of each mobile terminal by using FDM/TDM/CDM has been studied.
Use of a scheduled channel has been also studied as allocation of a synchronous random access SRA to physical resources (nonpatent reference 4).
A scheduled channel is scheduled to be allocated to each target mobile terminal, unlike a channel, such as an S-RACH, in which collision (or referred to as competition) of signals from a plurality of mobile terminals is allowed. In this case, because a region which is allocated in advance to each mobile terminal is decided, there is no competition between signals from a plurality of mobile terminals, and therefore there is no necessity for the ID number (the UE-ID) of each mobile terminal which is effective within the cell of the base station to be mapped onto an SR signal which each mobile terminal has transmitted. Therefore, in a case in which an uplink SRA is transmitted by using a scheduled channel, the amount of information of the uplink SR signal can be reduced.
A process of transmitting an Ack/Nack and a CQI, and an synchronous random access (an SR or the like) simultaneously in the case in which no uplink data transmission is carried out will be explained.
An uplink Ack/Nack and an uplink CQI are the ones which, when a mobile terminal is receiving downlink data from a base station, the mobile terminal transmits to the base station according to the status of the reception. In contrast, an SRA is the one which the mobile terminal transmits to the base station for an SR or the like before starting transmission of uplink data. Because the descriptions of these signals are independent from one another, there can be a case in which the mobile terminal transmits them simultaneously.
FIG. 26 shows an example in which a mobile terminal transmits an Ack/Nack and an SRA simultaneously in the case in which the mobile terminal is not carrying out any uplink data transmission.
This example is a case in which transmission of uplink data occurs while the mobile terminal carries out continuous reception of downlink data. The mobile terminal is receiving downlink data continuously. The data are demodulated and decoded in units of each TTI. The mobile terminal transmits result information (Ack/Nack) indicating a result of judgment of the reception to the base station according to the status of the reception of the downlink data. When receiving the transmission data normally from the base station, the mobile terminal transmits an Ack signal to the base station. The base station which has received the Ack transmits new data next time. In contrast with this, when not being able to receive the transmission data transmitted normally from the base station, the mobile terminal transmits a Nack signal to the base station. The base station which has received the Nack retransmits the data which the mobile terminal was not able to receive normally to the mobile terminal.
Allocation of the uplink Ack/Nack to physical resources is implemented by monopolistically allocating a plurality of time-frequency regions having separated narrow bands, as previously explained. Therefore, the uplink Ack/Nack is also transmitted continuously. In contrast, when uplink data occurs in the mobile terminal, the mobile terminal transmits a scheduling request SR to the base station before transmitting the uplink data. Allocation of the SR to physical resource is implemented by monopolistically allocating one certain time-frequency region, as previously explained. Therefore, as shown in the figure, when uplink data occur at a certain time, an SR occurs with a short time delay.
When the base station is not able to receive the SR signal which the mobile terminal has transmitted, the mobile terminal transmits the SR signal again. As can be seen from the above explanation, there occurs a status in which, when transmission of uplink data occurs while, for example, a mobile terminal carries out continuous reception of downlink data, the mobile terminal has to transmit an uplink Ack/Nack and an uplink SRA simultaneously. Furthermore, even though the mobile terminal does not receive the downlink data continuously, but receives the downlink data discontinuously, it is apparent that there may be a case in which the mobile terminal carries out the transmission of the uplink SR signal simultaneously if the mobile terminal transmits the uplink Ack/Nack which is a response to the received data.
Similarly, it can be considered that, also when a scheduled channel is allocated as allocation of the scheduling request SR, which the mobile terminal transmits to the base station, to physical resources, there occurs a status in which the mobile terminal have to transmit the uplink Ack/Nack and the uplink SRA simultaneously.
Nonpatent reference 4 describes nothing about what type of channel is used as a scheduled channel and how to allocate a time-frequency region as a physical resource. It is therefore understood that even if there is provided, for example, a channel in which a 1-bit physical resource intended only for a scheduling request SR is allocated, the mobile terminal has to transmit an uplink Ack/Nack continuously when carrying out continuous reception of downlink data, and therefore there occurs a status in which, when transmission of uplink data occurs at that time, the mobile terminal has to transmit an uplink Ack/Nack and an uplink SRA simultaneously.
Furthermore, the nonpatent reference 4 suggests nothing about “the problems of the invention” and “the advantages of the invention” which will be shown in the specification of the present invention.
Nonpatent reference 5 discloses transmitting an uplink scheduling request by using an individual uplink control channel, such as an existing channel (CQICH) for CQI transmission or an existing channel (ACHCH) for Ack/Nack transmission. The reference shows that, as a result, a transmission procedure of transmitting an uplink scheduling request with little delay (Delay) can be established.
However, the nonpatent reference 5 suggests nothing about “the problems of the invention” and “the advantages of the invention” which will be shown in the specification of the present invention.
The nonpatent reference 5 discloses only transmitting an uplink scheduling request by using either a channel (CQICH) for CQI transmission or a channel (ACHCH) for Ack/Nack transmission, but discloses nothing about how to allocate the CQICH and the ACHCH, as physical resources, to a time-frequency region. It is therefore understood that even if a case in which an uplink scheduling request is transmitted by using, for example, a channel (CQICH) for CQI transmission, is considered, when a mobile terminal is carrying out continuous reception of downlink data, the mobile terminal has to transmit an uplink Ack/Nack continuously, and therefore there occurs a status in which, when transmission of uplink data occurs at that time, the mobile terminal has to transmit an uplink Ack/Nack (ACHCH) and an uplink scheduling request (CQICH) simultaneously.
It is therefore understood that the nonpatent reference does not solve “the problems of the invention” shown in the specification of the present invention.
[Nonpatent reference 1] 3GPP contributions R1-062741
[Nonpatent reference 2] 3GPP contributions R1-062742
[Nonpatent reference 3] 3GPP TR25.814V7.0.0
[Nonpatent reference 4] 3GPP contributions R1-062719
[Nonpatent reference 5] 3GPP contributions R1-062571
Because conventional communication systems which comply with the LTE are constructed as mentioned above, an SC-FDMA (Single Career Frequency Division Multiple Access which is also referred to as DFT-spread OFDM) is used as an uplink access method. Because the SC-FDMA is single carrier transmission, compared with multi carrier transmission, such as OFDM, in which symbolic data are transmitted with them being piggybacked onto each subcarrier, the SC-FDMA has a feature of being able to reduce the PAPR (Peak to Average Power Ratio peak to average power ratio). Therefore, because the power consumption of a mobile terminal can be reduced at a time when the mobile terminal carries out transmission and the transmit power which satisfies defined adjacent channel leakage power can be increased, there is provided an advantage of widening the cell coverage. However, there may be a case in which a mobile terminal has to simultaneously carry out a process of transmitting an uplink Ack/Nack and an uplink CQI by using an Ack/Nack exclusive channel and a process of transmitting an uplink scheduling request signal (SR) by using an S-RACH or a scheduled channel, or a CQICH and an ACHCH according on its status. In this case, because those signals have no correlation among them, when transmitted simultaneously, they are not transmitted with single carrier transmission, but are transmitted with multi carrier transmission. In the case in which such signals having no correlation among them are transmitted simultaneously, the PAPR becomes high because the time waveforms of the transmission signals have a high peak. A problem is that as the PAPR becomes high, the power consumption of the mobile terminal increases and therefore the cell coverage becomes narrow. A further problem is that as the PAPR becomes high, those signals become an interference wave to other mobile terminals and the communication system.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a data communication method, a communication system, and a mobile terminal which can prevent increase in the radio resources load due to temporary increase in the physical channels and can also reduce the PAPR (peak to average power ratio).